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Functional consequences of P/Q-type Ca2+ channel Cav2.1 missense mutations associated with episodic ataxia type 2 and
Edwin Wappl1, Alexandra Koschak, Michael Poteser
1Institut für Biochemische Pharmakologie, Abteilung Pharmakologie und Toxikologie, Institut für Pharmazie, Universität Innsbruck, Peter-Mayrstrasse 1, A-6020 Innsbruck, Austria.
Abstract:
We have investigated the functional consequences of three P/Q-type Ca(2+) channel alpha1A (Ca(v)2.1alpha(1)) subunit mutations associated with different forms of ataxia (episodic ataxia type 2 (EA-2), R1279Stop, AY1593/1594D; progressive ataxia (PA), G293R). Mutations were introduced into human alpha1A cDNA and heterologously expressed in Xenopus oocytes or tsA-201 cells (with alpha(2)delta and beta1a) for electrophysiological and biochemical analysis. G293R reduced current density in both expression systems without changing single channel conductance. R1279Stop and AY1593/1594D protein were expressed in tsA-201 cells but failed to yield inward barium currents (I(Ba)). However, AY1593/1594D mediated I(Ba) when expressed in oocytes. G293R and AY1593/1594D shifted the current-voltage relationship to more positive potentials and enhanced inactivation during depolarizing pulses (3 s) and pulse trains (100 ms, 1 Hz). Mutation AY1593/1594D also slowed recovery from inactivation. Single channel recordings revealed a change in fast channel gating for G293R evident as a decrease in the mean open time. Our data support the hypothesis that a pronounced loss of P/Q-type Ca(2+) channel function underlies the pathophysiology of EA-2 and PA. In contrast to other EA-2 mutations, AY1593/1594D and G293R form at least partially functional channels.
Insights
Investigating P/Q-type Ca(2+) channel mutations reveals functional consequences for ataxia. Some mutations cause channel dysfunction, supporting loss-of-function as a cause of episodic ataxia type 2 and progressive ataxia.
Area of Science:
- Neuroscience
- Molecular Biology
- Genetics
Background:
- Ataxia, including episodic ataxia type 2 (EA-2) and progressive ataxia (PA), is linked to mutations in the alpha1A (Ca(v)2.1alpha(1)) subunit of P/Q-type Ca(2+) channels.
- Understanding the functional impact of these mutations is crucial for elucidating ataxia pathophysiology.
Purpose of the Study:
- To investigate the functional consequences of specific P/Q-type Ca(2+) channel alpha1A subunit mutations (R1279Stop, AY1593/1594D associated with EA-2, and G293R associated with PA).
- To determine if these mutations lead to a loss of channel function underlying ataxia.
Main Methods:
- Human alpha1A cDNA with specific mutations were expressed in Xenopus oocytes and tsA-201 cells.
- Electrophysiological analyses (current density, single channel conductance, current-voltage relationships, inactivation, recovery from inactivation) and biochemical analysis were performed.
Main Results:
- The G293R mutation reduced current density without altering single channel conductance.
- R1279Stop and AY1593/1594D mutations resulted in non-functional channels in tsA-201 cells, but AY1593/1594D showed partial function in oocytes.
- G293R and AY1593/1594D shifted the current-voltage relationship, enhanced inactivation, and AY1593/1594D slowed recovery from inactivation. G293R altered fast channel gating.
Conclusions:
- The findings support the hypothesis that a significant loss of P/Q-type Ca(2+) channel function contributes to the pathophysiology of EA-2 and PA.
- Unlike some other EA-2 mutations, AY1593/1594D and G293R mutations result in at least partially functional channels.